EPSC Abstracts Vol. 11, EPSC2017-131, 2017 European Planetary Science Congress 2017 EEuropeaPn PlanetarSy Science CCongress c Author(s) 2017

Comet Siding Spring's influence on the ’ ionosphere

O. Witasse (1), B. Sánchez -Cano (2), G. Molina-Cuberos (3), P.-L. Blelly (4), M. Lester (2), F. Leblanc (5), R. Modolo (5), J.-Y. Chaufray (5), G. Gronoff (6), J. Espley (7), M. Costa (1), and M. Giuranna (8)

(1) European Space Agency, Directorate of Science ([email protected]) (2) Department of Physics and Astronomy, University of Leicester, Leicester, UK (3) Departamento de Electromagnetismo y Electronica, University of Murcia, Murcia, Spain (4) Institut de Recherche en Astrophysique et Planétologie, Toulouse, France (5) LATMOS, Paris, France (6) Science Directorate, Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, , USA (7) Laboratory for Planetary Magnetospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA (8) Istituto Nazionale di Astrofisica, Roma, Italy

Abstract 44 hours before the comet closest approach, disturbing the Mars’ plasma environment [1]. Many On October 19th 2014, Mars experienced a close solar flares also occur in this period, some of them encounter with Comet C/2013 A1 (Siding Spring), at could have hit Mars. Moreover, this cometary flyby a distance of ~138,000 km. The coma washed over took place at the start of a dust season, as indicated Mars and the planet passed directly through the by Mars Express PFS dust opacity measurements and cometary debris stream, producing significant effects data assimilation [13,14]. in Mars’ upper atmosphere. We present here an overview of ionospheric measurements performed Obviously, this context implies that the data analysis during the comet encounter with Mars Express, is not trivial. MAVEN, and Mars Reconnaissance Orbiter. We discuss the comet’s influence on the ionosphere 3. Measurements and data sets through different processes that work at different altitudes: magnetospheric disturbances, impact of The following data sets are used in this study: Data cometary pick-up ions, and deposition of cometary recorded by the MARSIS radar aboard Mars Express dust. in the active ionospheric mode [2] give access to local densities at the altitude, 1. Geometry and timing of the electron density profiles and an indication of the signal attenuation (due to present at low comet encounter altitudes [3]). The data recorded by the SHARAD radar aboard Mars Reconnaissance Orbiter give The closest approach with comet Siding Spring took access to the Total Electron Content [4]. The data place at a distance of ~138,000 km from the center of recorded by the MAVEN orbiter include information Mars, on 19 October 2014 at 18:28 UT (Solar on the magnetic field [5], the metallic ions longitude Ls 217, Martian Year 32). It flew by Mars originating from the comet [6,7], and energetic at a relative velocity of ~56 km/s, moving from South particles possibly identified as pick-up ions [8]. to North (retrograde orbit, 129 degrees inclination). 4. Effects on the Mars’ ionosphere 2. Context of the comet encounter The interaction of the Siding Spring coma and the The context is essential to properly analyse the data Mars’ ionosphere can be characterized by several taken during this unique event. Since we are dealing processes. First, the magnetosphere was severely here with dust and upper atmosphere, it is important distorted during the comet’s passage [5]. As a to characterise the space weather and the seasonal consequence, we can expect some disturbances in the dust contexts. topside ionosphere. A second effect is the flux of pickup O+ ions originating from the coma interacting The space weather conditions are peculiar: a large with the solar wind. These pickup ions precipitate interplanetary coronal mass ejection hit Mars about primarily on the dayside hemisphere and can increase ionospheric densities around 110-120 km altitude Comparison of its Forbush decreases at 1.4, 3.1 and 9.9 [9,10]. Finally, the cometary dust is deposited in the AU, submitted to JGR, 2017 atmosphere, mainly below 100 km altitude, and is responsible for the formation of a low altitude [2] Gurnett, D. A., et al. (2015), An ionized layer in the ionospheric layer [2,6,7,11]. upper atmosphere of Mars caused by dust impacts from comet Siding Spring, Geophys. Res. Lett., 42, doi:10.1002/ 2015GL063726. These mechanisms and effects are discussed and compared, with the support of modeling and data [3] Witasse, O. et al (2001), HF radio wave attenuation due analysis. In particular, we propose some explanations to a meteoric layer in the atmosphere of Mars, Geophys. to understand those ionospheric compressions and Res. Lett., 28, 3039–3042, doi:10.1029/2001GL013164. bulges observed in the Mars Express data set (see Figure 1), and explore the complex interaction dust- [4] Restano, M., et al. (2015), Effects of the passage of ionosphere. Comet C/2013 A1 (Siding Spring) observed by the Shallow Radar (SHARAD) on Mars Reconnaissance Orbiter, Geophys. Res. Lett., 42, doi:10.1002/2015GL064150.

[5] Espley, J. R., et al. (2015), A comet engulfs Mars: MAVEN observations of comet Siding Spring’s influence on the Martian magnetosphere, Geophys. Res. Lett., 42, doi:10.1002/2015GL066300.

[6] Benna, M., et al. (2015), Metallic ions in the upper atmosphere of Mars from the passage of comet C/2013 A1 (Siding Spring), Geophys. Res. Lett., 42, doi:10.1002/2015GL064159.

[7] Schneider, N. M., et al. (2015), MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars, Geophys. Res. Lett., 42, doi:10.1002/2015GL063863. Figure 1: Mars Express MARSIS electron density profiles obtained within 5 minutes of difference from [8] Sánchez-Cano, B. et al., Energetic particle showers over the orbit at the time of the comet closest approach, on Mars from comet Siding-Spring, EPSC 2017 abstract the dayside hemisphere. Left panel: electron density [9] Gronoff, G., et al. (2014), The precipitation of keV profile showing two bulges centered around 200 and energetic oxygen ions at Mars and their effects during the 240 km. The solar zenith angle is 71 degrees. Right comet Siding Spring approach, Geophys. Res. Lett., 41, panel: electron density profile where a clear 4844–4850, doi:10.1002/2014GL060902. compression of the ionosphere is found above 180 km. The solar zenith angle is 80 degrees. In both [10] Wang et al., Cometary sputtering of the Martian panels, the NeMars model [12] was plotted to atmosphere during the Siding Spring encounter, Icarus 272 compare with a predicted and undisturbed (2016) 301–308 ionosphere. [11] Molina-Cuberos et al. Meteoric ions in the atmosphere Acknowledgements of Mars, Planetary and Space Science 51 (2003) 239 – 249 [12] Sánchez-Cano, B., et al. (2013), NeMars: An B.S.-C. and M.L. acknowledge support through empirical model of the Martian dayside ionosphere based STFC grant ST/N000749/1. on Mars Express MARSIS data, Icarus, 225, 236–247, doi:10.1016/j.icarus.2013.03.021. References [13] Giuranna, M. et al., EPSC 2017 abstract [1] Witasse et al., Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov- [14] Montabone, L., et al., Eight-year Climatology of Dust Gerasimenko, Saturn, and en-route to Pluto. Optical Depth on Mars, Icarus (2015), doi: http://dx.doi.org/10.1016/j.icarus.2014.12.034